Induction apparatuses comprise at least one induction surface upon which a vessel may be disposed and heated, said apparatuses comprising at least one induction coil disposed beneath the induction surface in order to heat said vessel. To heat the vessel, the induction coil is supplied by an alternating current. A magnetic field is generated as a result and this causes the generation of eddy currents through the vessel disposed on the induction surface, said eddy currents causing said vessel to heat up.
There are various known alternatives for supplying the induction coil, the majority of which include a rectifier and a frequency converter for the rectified signal. The frequency converter generally comprises at least one switch, and in many cases a single switch is used, this being connected in series with a parallel resonant circuit formed by the induction coil and a capacitor.
The drawback with this alternative is that it may cause the system to overheat or become damaged due to the use of a vessel made of an unsuitable material such as aluminium, for example, a material which offers high inductance and low resistance. It is important, therefore, that the induction apparatus includes a method capable of detecting the presence or absence of said vessel, and/or the quality (resistivity) (or size) of said vessel, the purpose being not to supply said induction coil with power when no vessel is disposed on the induction surface for example, or to supply it with power that is insufficient for the size or resistivity of the vessel disposed on said surface.
European Patent Application published as EP1935214A2 discloses an induction apparatus that comprises a method for detecting a vessel. In this method the voltage in an intermediate node between the switch and the parallel resonant circuit formed by a capacitor and the induction coil is determined, and it is important to close the switch when the voltage in the intermediate node reaches a minimum point and for a time interval determined by the voltage in said minimum point. The closure of the switch generates oscillations in the voltage of the intermediate node, and the presence or absence of the vessel is determined in accordance with the number of oscillations detected.